The invention relates to a method of selectively providing a pattern of a material other than glass on a glass substrate by electroless metallization, the pattern and the glass substrate being brought into contact with an aqueous Pd sol after which the pattern is metallized in an electroless metallization bath.
Such a method is used in, for example, the manufacture of electro-optical display devices in which a substance is present between two glass substrates, which substance is subject to an optically perceptible physical change under the influence of an electric field. In such devices, transparent electrodes are present on at least one of the substrates, the second substrate may also be transparent and provided with transparent electrodes. A known display device of this type is, for example, an LCD cell. In the case of such a cell, a liquid-crystalline medium is present between two parallel glass plates. Transparent electrodes are provided on the sides of the glass plates facing the medium, said electrodes generally consisting of a semiconductive metal oxide such as indium-III-oxide and tin-IV-oxide. Such layers, which generally have a thickness of approximately 150 nm, can be provided on the glass plates by sputtering or vacuum evaporation. Such layers can alternatively be provided by Chemical Vapor Deposition or by hydrolysis and pyrolysis of a corresponding metal compound. At present, preferably, layers of indium oxide doped with tin oxide are used, which are generally referred to as ITO. The desired electrode pattern can be obtained by etching the ITO layer according to a pattern. Alternatively, the electrodes can be directly provided on the glass according to the desired pattern, for example, by vacuum evaporation or sputtering according to a pattern using a mask.
The electrodes of such a display device are connected, via conductor lines which also consist of ITO, to contact faces, also consisting of ITO, in order to electrically connect the electrodes to the drive of the display device. For this purpose, ICs can be secured to these contact faces. However, a properly adhering electric connection between the ICs and the contact faces of ITO cannot be obtained directly by soldering nor in any other way. To obtain a properly adhering electric connection, the surfaces serving to establish the electric connection and the parts of the conductor lines which form the connection between the contact faces and the actual electrodes must first be covered with a metal coating. Said metallization also serves to reduce the electric resistance in situ. A suitable method of metallizing ITO consists in immersing the portion to be plated in an electroless metallization bath. This requires the previous activation of the portion to be metallized in an activation treatment. A customary activation treatment for an electroless metallization process consists in successively immersing SnCl.sub.2, AgNO.sub.3 and PdCl.sub.2 in aqueous solutions. The Pd nuclei formed on the surface catalyze the electroless metallization process. A disadvantage of such an activation treatment is that, in general, only the glass is provided with Pd nuclei, not the ITO. As a result thereof, only the glass substrate is metallized in a subsequent metallization process.
U.S. Pat. No. 4,824,693 discloses a method of selectively depositing ITO lines on a glass substrate in an electroless metallization process. To activate the ITO surface, the substrate is immersed in a colloidal Pd solution which has been obtained by mixing SnCl.sub.2 and PdCl.sub.2 solutions. The activating solution obtained contains a sol of metallic Pd particles which are stabilized by a Sn.sup.4+ outer sheath. Since such Pd particles also activate the glass, the glass has to be deactivated before carrying out the electroless metallization process. Deactivation takes place in an aqueous solution of hydrogen fluoride (HF).
A disadvantage of the known method is that it requires additional processing steps, i.e. a deactivation step in a HF solution and an associated rinsing step. A further disadvantage of deactivation using a HF solution resides in the fact that the glass substrate is attacked and/or underetching of the ITO tracks takes place. Still another disadvantage of the known method is the poor adhesion of the electrolessly deposited metal layer to the ITO tracks.